Groundwater

Groundwater

• Diana L. Duckworth

• Rustburg High School

• Campbell County Schools

Key Concepts

• Porosity: percentage of the rock that is empty space

• Depends on grain size, shape, & sorting

• Permeability: ability of a rock to yield water

• Depends on grain size (larger grains have larger pores), grain shape, & sorting
• Large pores, less impact of friction
• Rounded grains, larger pores
• Poor sorting, small grains fill in pores & reduce permeability

Water table reaches surface at springs, rivers, & lakes

• Water table follows the shape of the land.

• Water flows downhill underground.

Man’s Usage of Groundwater

• Two kinds of wells:

• Ordinary well that requires pumping
• Artesian well where water rises to surface without pumping

Ordinary Wells

• Two water levels

• Static water level
• Pumping water level

Problems with Overexploitation

• Withdrawals in excess of recharge rates:

• Artesian wells lose pressure, must be pumped
• Ordinary wells can produce overlapping cones of depression
• Lead to dewatering of aquifer
• Lower stream levels in drought
• Salt water intrusion in coastal areas

Groundwater Budget

• Income = precipitation

• Outgo = runoff + evapotranspiration

• Surplus: precipitation is greater than evapo-transpiration & runoff

• Water table rises

• Deficit: precipitation is less than evapo-

• transpiration & runoff

• Water table falls

• Steady state: precipitation = evapotranspiration & runoff

• Water table stays steady

• Water Balance Equation P = E + R + G

• Where G = change in water table

Caves

• CO2 dissolves in groundwater

• Becomes acidic
• Dissolves limestone
• Joints enlarged into caves

• Dry caves

• Dripping water evaporates
• Creates stalactites & stalagmites

Sinkholes

• Roof of cave collapses

• Leaves circular depression
• May fill with water

Groundwater Topography

• Karst topography

• Sinkholes
• Caverns
• Disappearing streams
• Ponds with no surface outlet
• Limestone terrain